1. Field of the Invention
The present invention relates to a projector of a reflection type. More particularly, the present invention relates to a projector of a reflection type having a body, where an image of a transparency can be projected, has a small height.
2. Description Related to the Prior Art
An overhead projector is an apparatus for presentation to a great number of onlookers or audience with an image of a transparency in an enlarged size on a screen. It is known to use a liquid crystal display (LCD) panel of a transmittance type in combination with the overhead projector. The LCD panel projects a video image, such as a motion picture image, to a screen, and also smooths an operation of setting one image after another. An example of the LCD panel consists of a twisted nematic (TN) type of liquid crystal device, and is placed on a stage of the overhead projector. The LCD panel is connected to a video player, a microcomputer, or the like to receive an input of an image, and displays the image in the form of a motion picture or computer-graphic (CG) image.
There are suggestions of an LCD-fitted overhead projector in which the LCD panel is built in the overhead projector. In the LCD-fitted overhead projector, the LCD panel of the twisted nematic type is contained in the stage of the overhead projector. There is also a proposal of using a nematic-cholesteric phase-transition (NCPT) type of the LCD panel in the LCD-fitted overhead projector. The LCD panel of the nematic-cholesteric phase-transition type is characteristically capable of having a maximized optical transmittance as high as 80-90%. This is advantageous as high contrast and sharpness are obtained in projecting an image of the LCD panel or the transparency.
The overhead projector herein is a reflection type more recent than a transmittance type of overhead projector. The transmittance-type projector contains a light source in its base. The transparency is illuminated by the light source directly in an upward direction. The disposition of the light source in the transmittance-type projector is a short-coming as it enlarges the height of the projector. The reflection type of the overhead projector has the light source contained in the rear of a projector head as a top of the projector. The illuminating light is initially passed down to the transparency, and is reflected upward to the projector head upon illuminating the transparency. The reflection type is more advantageous over the transmittance-type projector, as the height of projector is the smaller because of the disposition of the light source.
In FIG. 4, a reflection type of LCD-fitted overhead projector 2 is illustrated. The overhead projector 2 includes a stage 7 and a stay 8 disposed erectly from the stage 7. The stage 7 includes a Fresnel lens 3, a liquid crystal display (LCD) panel 4, an illuminating mirror 5 and a driver circuit board 6, which are overlaid on one another. The LCD panel 4 is a nematic-cholesteric phase-transition type. The stay 8 supports a light source 9, a condenser lens 10, path converter mirrors 11 and 12 and a projector head 14. The projector head 14 includes a projection lens 13.
In the overhead projector 2, the light from the light source 9 of the projector head 14 is reflected not only by the illuminating mirror 5 but by a surface of the Fresnel lens 3. This additional partial reflection of the surface of the Fresnel lens 3 does not affect a projecting operation of an image of the LCD panel 4, but affect a projecting operation of an image of a transparency 16, as depicted in the enlarged drawing. The reflected light from the surface of the Fresnel lens 3 illuminates the transparency 16. Due to a considerable thickness of the LCD panel 4 between the Fresnel lens 3 and the illuminating mirror 5, the light reflected by the illuminating mirror 5 is remarkably deviated from the light reflected by the surface of the Fresnel lens 3. A double-projection phenomenon occurs, as an image is projected in a double manner on a screen 17.